The present invention relates to a posterior chamber lens implant for use after extra-capsular cataract surgery.
In extra-capsular surgery, a surgical opening is formed through the front membrane or anterior capusle of the lens of the human eye and the cataracted lens is surgically removed. During such surgery, however, it is important to leave the posterior capsule of the lens intact so that it forms a barrier between the vitreous humor and the aqueous humor.
Following the removal of the cataract it is often desirable to replace the human lens with an artificial lens implant in order to restore sight to the eye. It has been found that posterior chamber lens implants are considered by some surgeons to be medically superior to anterior chamber and pupil lens implants.
In such posterior chamber lens implants, the optic is typically secured in place in the posterior chamber by loops or haptics extending outwardly from the optic and seating either in the cul-de-sac of the anterior and posterior capsule or in ciliary sulcus of the eye.
In a high incidence of cases, after a period of time following implantation of the lens, the posterior capsule becomes clouded and obscures vision. In order to restore the vision to the eye after this has occurred, it is necessary to perform a posterior capsulotomy to remove the portion of the posterior capsule that is behind the optic.
Recently it has become popular to use laser posterior capsulotomy in which a laser is focused on the posterior capsule through the pupil. Upon activation of the laser, the laser causes an opening through the posterior capsule behind the optic to be made, thus, restoring vision to the eye.
At present, however, laser posterior capsulotomies can be safely performed only with specially configurated lenses which, however, exhibit some disadvantageous optical characteristics as a result of their special configurations. It must be remembered, in this connection, that the conventional posterior chamber lens is implanted with its flat rear face in contact with the posterior capsule. Consequently, there is a substantial risk of damaging the optic while performing laser capsulotomy on the membrane of the eye which is in contact with the rear face of the optic. One lens which has been designed specifically for laser capsulotomy, but which has some of the optical disadvantages alluded to above, is the lens described in my own U.S. Pat. No. 4,495,665. While the rearward projections of a lens according to my said patent provide adequate spacing of the posterior capsule from the mid-portion of the rear face of the optic, nevertheless, because of their location in the path of light being transmitted through the optic to the retina of the eye, the projections, according to my patent, tend to reduce the effective size of the optic for light transmissibility and may interfere in some other ways, for example, slight distortions of the vision of the eye.
Another known posterior chamber lens capable of spacing portions of the rear face of an optic from the posterior capsule is the lens described in the patent to Hoffer U.S. Pat. No. Re. 31,626. That patent discloses an annular lip projecting rearwardly from the rear face of the optic for providing the desired spacing. This construction suffers from the very same infirmities, even more exaggerated, which I have just described with respect to my own patent. Thus, the Hoffer annular lip tends to substantially reduce the effective size of the optic since it also is interposed in the region through which light is transmitted through the optic to the retina, resulting furthermore in the possibility of substantial distortion in the vision of the eye. A still further known posterior chamber lens capable of spacing portions of the rear surface of an optic from the posterior capsule is the lens described in the patent to Myers U.S. Pat. No. Re. 31,998. That patent discloses an optic having a concave rear surface as a result of which the central portion of such rear surface is spaced from the posterior capsule when the surrounding annular peripheral portion of the optic is in contact with the posterior capsule. The optics according to this construction are, however, very difficult and costly to make free of optical distortion. Since the distortion introduced by the rear concave surface must be compensated for very accurately by the convex anterior surface.